Piezoelectric ink jet printer head and its manufacturing process

ABSTRACT

Disclosed is a piezoelectric ink jet printer head in which a chamber and an ink storage are integrally formed. A process for manufacturing the ink jet printer head is also disclosed. The ink jet printer head formed by laminating a plurality of plates includes: a) an actuator portion being composed of upper and lower electrodes, a piezoelectric plate inserted between the upper and lower electrodes, a protection layer placed on the upper electrode, and a resilient plate disposed beneath the lower electrode; b) an ink passage portion composed of a spacer disposed beneath the resilient plate and forming a side portion of a chamber, a channel plate disposed beneath the spacer, the channel plate forming an ink passage in one side of the chamber and simultaneously expanding the chamber, and a nozzle plate disposed beneath the channel plate, the nozzle plate forming the lower side of the chamber and having a nozzle communicating with the chamber; and c) an ink-supplying portion formed by a through-hole reaching the ink passage of the channel plate through the actuator portion and the spacer.

CROSS-REFERENCED APPLICATIONS

The present application claims priority under 35 U.S.C. 119 and 35U.S.C. 365 to Korean Patent Application No. 10-2003-0039048 filed onJun. 17, 2003 and PCT Application No. PCT/KR2004/001080 filed May 11,2004, which are both hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a piezoelectric ink jet printer headand a process for manufacturing the same. Specifically, the inventionrelates to an ink jet printer head in which a chamber and an ink storageare integrally formed inside the ink jet printer head.

BACKGROUND ART

In general, the ink jet printing is carried out by discharging liquidink on a print paper. In other words, the ink jet printer head isprovided with arrayed nozzles each having a size of needle tip, fromwhich the liquid ink is sprayed towards the print paper. Although thebasic principle is same, the ink jet printing is categorized into abubble jet type, a thermal jet type and a piezoelectric type accordingto the ink discharging mode.

In the bubble jet spraying type, a heater disposed on the side wall of amicro tube controls the size of bubbles in order to spray ink. That is,the heater is operated to generate bubbles, and then the ink is sprayedwhen the bubble is expanded to its maximum size. After spraying, if theheating is stopped, ink is newly supplied as the bubble is diminished.This type of ink jet printing is advantageous in that it does not needan ink storage and a small sized head can be realized since the tube andheater are very small. However, it is very difficult to array thenozzles in a two-dimensional pattern.

The thermal jet type is similar to the above-mentioned bubble jet, butthe position of a heater is different therefrom. In this type, theheater is disposed on the same or opposite side of the nozzle, and whenthe heated ink is vaporized, the ink is sprayed due to the vaporpressure thereof. Therefore, one of the biggest advantages of this typeresides in that the heater and nozzle can be arrayed in atwo-dimensional pattern, and therefore, it is relatively easy toincrease the number of nozzles.

In the piezoelectric spraying type, ink is discharged by an impact frombehind a nozzle according to an input signal as in the conventionalsyringe operation. As the driving force for discharging ink, apiezoelectric element is employed, which changes its shape in responseto voltage variation. Specifically, when a voltage is applied, thepiezoelectric element is deformed and the liquid surface at the tip ofthe nozzle is swollen. Instantly, if the liquid surface is pulled backby controlling the voltage, then ink ahead of the nozzle face is sprayedforward due to its momentum.

Among the above-described types, the bubble jet and thermal jet typesnecessitate a relatively small space for the heater for generating theink spraying force, as compared with the actuator in the piezoelectricspraying type. Furthermore, in the bubble and thermal jet types, an inkchamber and an ink storage may be disposed on the same plane so that thedensity of nozzles can be fairly increased. In contrast, thepiezoelectric type has a disadvantage in that the number of nozzles orthe nozzle density cannot be readily increased due to the complicatedstructure thereof.

FIG. 1 shows a schematic configuration of the conventional piezoelectricink jet print head, which is exemplified by U.S. Pat. No. 5,748,214.

As depicted in FIG. 1, the conventional ink jet printer head is composedof a port for supplying ink (not shown), an ink storage 42 for storingthe ink supplied through the port (not shown), a chamber 15 forreceiving ink from the ink storage 42, a nozzle 21 for discharging inkfrom the chamber 15, and an actuator for exerting pressure to thechamber, i.e., the ink therein in order to discharge the ink through thenozzle 21 via a nozzle connection 20.

The above-mentioned actuator includes a resilient plate 13, a lowerelectrode 16 disposed on the resilient plate 13, a piezoelectric plate17 disposed on the lower electrode 16, and an upper electrode 18 placedon the piezoelectric plate 17.

The chamber 15 is defined by the resilient plate 13 disposed thereabove,a spacer 12 placed in the side thereof, and a sealing plate 11 placedtherebelow.

In addition, the ink storage 42 is constituted by an ink supplying plate24 where upper through-holes 26 and 40 are formed, an ink storageforming plate 23 on the side thereof, and a nozzle plate 30 disposedtherebelow. The nozzle for spraying ink is formed in the nozzle plate30.

In operation, when an electric power is applied to the actuator, thepiezoelectric plate 17 is deformed and exerts a pressure to the chamber15, and thus, the ink inside the chamber 15 is discharged through thenozzle 21 due the pressure applied thereto.

On the other hand, U.S. Pat. No. 6,217,158B1 discloses an ink jetprinter head similar to the above-described patent, except that it doesnot have the resilient plate disposed below the lower electrode.

The above-mentioned conventional ink jet printer heads embrace severalproblems and disadvantages. The conventional head necessitates aseparate ink storage and, therefore, cannot use the space and areaefficiently so an efficient arrangement of elements or components can bereadily achieved. Also, this results in significant reduction in thenumber of nozzles, i.e., the nozzle density.

In addition, the nozzle portion is formed by laminating plural plates,and the ink storage must be included, together with the nozzle portion,in the structure formed by the lamination of plates. This causes acomplexity in the fabricating process, and deteriorates its spaceefficiency.

Another drawback is caused by the fact that the cross section leading tothe nozzle portion from the chamber is steeply changed. Therefore, itimposes an inevitable limitation in generating fine ink drops.

Furthermore, the ink-supplying path from the port to the chamber isdisadvantageously bent, so that the ink bubbles (F) are apt to betrapped in the ink-supplying path.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide an ink jet printerhead, in which a chamber and ink storage are integrally formed, therebyenabling a simple structure of the ink jet printer head.

Another object of the invention is to provide an ink jet printer head,in which a nozzle is formed of a single plate so that the manufacturingprocess can be simplified, while improving the space efficiency.

A further object of the invention is to provide an ink jet printer head,in which the cross section leading to the nozzle from the chamber variessuch that the amount of ink to be sprayed can be readily controlled,thereby allowing for the spraying of finer ink drops.

A further object of the invention is to provide an ink jet printer head,in which the ink is supplied directly to each individual chamber viaeach through-hole and ink passage provided in the side of the chamber,without necessity of a separate ink storage. Therefore, the space andarea, which otherwise is occupied by a conventional ink storage, can besaved, and the actuator and nozzle portion are arrayed in atwo-dimensional fashion, thereby increasing the number of nozzles, i.e.,the nozzle density.

A further object of the invention is to provide an ink jet printer head,in which the ink is supplied directly to each individual chamber viaeach through-hole and ink passage provided in the side of the chamber.Therefore, the size of the chamber can be reduced and the ink passagewaycan be simplified, thereby significantly reducing the possibility ofentrapping ink bubbles therein.

To accomplish the above objects, according to one aspect of the presentinvention, there is provided an ink jet printer head formed bylaminating a plurality of plates. The ink jet printer head of theinvention includes: (a) an actuator portion being composed of upper andlower electrodes, a piezoelectric plate interposed between the upper andlower electrodes, a protection layer placed on the upper electrode, anda resilient plate disposed beneath the lower electrode; (b) an inkpassage portion composed of a spacer disposed beneath the resilientplate and forming a side portion of a chamber, a channel plate disposedbeneath the spacer, the channel plate forming an ink passage in one sideof the chamber and simultaneously expanding the chamber, and a nozzleplate disposed beneath the channel plate, the nozzle plate forming thelower side of the chamber and having a nozzle communicating with thechamber; and (c) an ink-supplying portion formed by a through-holereaching the ink passage of the channel plate through the actuatorportion and the spacer.

Here, preferably, a tapered portion is formed above the nozzle such thatthe cross section of the chamber varies from the chamber to the startingpoint of the nozzle.

The ink jet printer head is provided with an ink container above theprotection layer. A plurality of ink jet head modules may be arrayed ona same plane in a matrix fashion, in which each module is composed ofthe actuator portion, the ink passage portion and the ink-supplyingportion. The ink is supplied to the chamber of each ink jet head modulefrom the ink container through each through-hole and ink passage. In theconventional piezoelectric ink jet printer head, only a 2×2 matrixarrangement is allowed, but in the invented ink jet printer head,various and unlimited number of rows and columns can be achieved withoutsuch limitation in the conventional one.

Furthermore, the resilient plate is formed of ZrO₂ having a goodmaterial property, or BaTiO₃ being easily formed in the shape of thinfilm. Al₂O₃ may also be employed.

According to another aspect of the invention, there is also provided aprocess for manufacturing a piezoelectric ink jet printer head, which isformed by laminating a plurality of plates including a resilient platehaving elasticity, a nozzle plate having a nozzle, and the like. Theprocess of the invention includes the steps of: (a) disposing aresilient plate; (b) printing a lower electrode on the resilient plate;(c) printing a spacer beneath the resilient plate; (d) printing achannel plate beneath the spacer; (e) sintering the assembly of theresilient plate, the lower electrode, the spacer and the channel plate;(f) forming a piezoelectric plate on the lower electrode; (g) forming anupper electrode on the piezoelectric plate; (h) forming a protectionlayer on the upper electrode; (i) forming a through-hole leading to thespacer from the protection layer; (j) forming a tapered portion in thenozzle plate; (k) forming a micro-spray hole at the apex of the taperedportion in the nozzle plate; and (l) bonding the nozzle plate and thechannel plate to each other.

BRIEF DESCRIPTION OF DRAWINGS

Further objects and advantages of the invention can be more fullyunderstood from the following detailed description taken in conjunctionwith the accompanying drawings in which:

FIG. 1 shows a schematic configuration of the conventional piezoelectricink jet print head;

FIG. 2 is a top plan view and cross-sectional view of the ink jetprinter head according to one embodiment of the invention;

FIG. 3 is a top plan view and cross-sectional view illustrating anembodiment of the ink jet printer head arrangement according to theinvention; and

FIG. 4 is a block diagram showing a manufacturing process of thepiezoelectric ink jet printer head according to one embodiment of theinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to the accompanying drawings, the preferred embodimentsaccording to the present invention are hereafter described in detail.

FIG. 2 is a top plane view and cross-sectional view of the ink jetprinter head according to one embodiment of the invention. Referring toFIG. 2, the ink jet printer head of the invention is composed of an inkpassage portion for receiving ink and spraying it through a nozzle, andan actuator portion for exerting a pressure to the ink to discharge itthrough the nozzle, and an ink supplying portion for supplying inkthrough a through-hole.

The above-mentioned ink passage portion is constituted by a nozzle plate52 disposed at the lowermost thereof, a channel plate 56 disposed on thenozzle plate 52, and a spacer 72 disposed on the channel plate 56.

The nozzle plate 52 is provided with a nozzle 52 a formedfluid-communicatively in the upper and lower directions. A taperedportion 54 is formed at the upper part of the nozzle 52 a.

The channel plate 56 is connected with the space 72 in the upperdirection, and connected with the tapered portion 54 in the lowerdirection to thereby expand the internal space of the chamber 78. An inkpassage 58 is formed at one side of the channel plate 56.

The actuator portion is composed of a resilient plate 70 disposed at thelower part thereof, a lower electrode 60 disposed on the resilient plate70, a piezoelectric plate 62 disposed on the lower electrode 60, anupper electrode 68 on the piezoelectric plate 62, and a protection layer66 formed on the upper electrode.

Here, the spacer 72 constituting the uppermost part of the ink-supplyingportion is coupled with the resilient plate 70, i.e., the lowermost partof the actuator portion such that the chamber 78 is defined by theresilient plate 70 as an upper wall, the spacer 72 and the channel plate56 as a side wall, and the nozzle plate 52 as a lower wall.

As shown in FIG. 2, the ink-supplying portion as described above isconstituted by an ink container (not shown) provided at the upper partthereof for supplying ink to the chamber 78, and a through-hole 64,which is fluid-communicatively formed from the ink container (not shown)to the ink passage 58 through the actuator portion and the spacer 72.

On the other hand, the protection layer 66 is provided with an electrodepad 74 at one side thereof, through which an external control circuit(not shown) is electrically connected with the ink jet printer head ofthe invention.

FIG. 3 is a top plan view and cross-sectional view illustrating anembodiment of the ink jet printer head arrangement according to theinvention. Referring to FIG. 3, the ink jet printer head of theinvention is composed of nine modules arrayed in the same plane in a 3×3matrix pattern, in which each module is defined by the ink jet printerhead illustrated in FIG. 2. A 3×3 matrix arrangement is illustrated inFIG. 1, but not limited thereto. For example, a 20×20 or 30×40 matrixpattern or the like may be achieved according to the present invention.With the conventional piezoelectric ink jet printer head, only a 2×2matrix arrangement is allowed, but according to the invention, there isno limit. In other words, various and unlimited number of rows andcolumns can be achieved, depending on the design of the ink jet printerhead.

FIG. 4 is a block diagram showing a manufacturing process of thepiezoelectric ink jet printer head according to one embodiment of theinvention.

First, a ZrO₂ green sheet having a thickness of 3 μm is prepared anddisposed by a tape-casting or a doctor-blade process (step S110). TheZrO₂ green sheet is employed as a resilient plate. As preferredmaterials for the resilient plate, BaTiO₃ and Al₂O₃ and the like may beemployed, along with ZrO₂. The BaTiO₃ material can be easily made in theform of a thin film, and the Al₂O₃ material has good thermalcharacteristics. Next, a lower electrode is printed on the green sheet(step S112). Then, a spacer is printed in a thickness of 120 μm beneaththe green sheet (step S114). After that, a channel plate is printed in athickness of 40 μm beneath the spacer (step S116). The spacer andchannel plate is preferably made of the same material as the resilientplate.

Next, the layered structure described above is sintered at 1200° C. inorder to improve the rigidity and the bondability between layers.

Then, a piezoelectric plate having a thickness of 1.5-6 μm is formed onthe lower electrode (step S120). The piezoelectric plate is preferablymade of a PZT material. The piezoelectric plate may be formed employinga sputtering technique, a sol-gel method, or a metal organic chemicalvapor deposition (MOCVD). In case of a piezoelectric plate having athickness of above 2 μm, it has been found that the MOCVD is mostpreferred. On the other hand, a required portion of the piezoelectricplate may be etched in order for the lower electrode to be connectedwith an external control circuit (not shown).

Afterwards, an upper electrode is formed on the piezoelectric plate(step S122). The upper electrode may be formed using a sputteringtechnique, a metal organic chemical vapor deposition (MOCVD), avaporization method or the like. On the other hand, by using anappropriate patterning process (for example, lithography, lift-offprocess), each actuator constituting the ink jet printer head can beseparated and an electrode pad 74 may be formed in order to connect theexternal control circuit (not shown) thereto.

After forming the upper electrode, a protection layer is formed on theupper electrode (step S124). The protection layer may be formed byvapor-depositing SiO₂ using a chemical vapor deposition method (CVD).Then, in order to compensate for deterioration of the piezoelectriclayer due to hydrogen, the piezoelectric layer may be heat-treated. Onthe other hand, a desired portion of the protection layer may be etchedto expose the pad portion in the upper electrode to the outside. Theprotection layer functions to protect the actuator electrically andchemically from an ink solution, and an ink container (not shown) isinstalled right above the protection layer. In addition, appropriatesealing means for example, an o-ring having a resistance to the ink oran adhesive such as epoxy may be used. On the other hand, the inkcontainer can contain ink or be provided with a port, through which inkcan be supplied into the internal space thereof from an external inkcontainer.

After completing the formation of the protection layer, a through-holeis formed which passes through the protection layer, the piezoelectricplate, the lower electrode, the resilient plate, and the spacer (stepS126). The through-hole may be formed by means of a supersonic process,a micro-drilling method, a micro-blasting using an abrasive, or thelike. Here, the diameter and depth of the through-hole are preferred tobe 30 μm and should be under 150 μm, respectively.

Next, a tapered portion is formed in the nozzle plate (step S128). Thenozzle plate is preferred to be formed of stainless steel or siliconmaterial, and may be formed by means of a supersonic process, amicro-drilling, an anisotropic etching (in case of silicon material), orthe like.

Thereafter, a micro-spray hole is formed at the tip of the above-formedtapered portion to constitute a nozzle (step S130). Preferably, aconcentrated ion-beam may be used for forming the micro-spray hole.

In the final step, the nozzle plate is bonded to the channel plate usingan adhesive (step S132). An elastic epoxy or the like is preferably usedas the adhesive. When the bonding is completed, the process formanufacturing the ink jet printer head according to the invention isfinished.

The operation of the ink jet printer head having the above-describedconstruction according to the invention will be explained below.

First, ink is injected through the through-hole 64 formed at the upperportion of the ink jet printer head, and under its gravity, fallsdownwards to be collected in the chamber 78 via the ink passage 58.

The ink collected in the chamber 78 remains inside the chamber due to anattraction force between ink molecules, without discharging through thenozzle 52 a.

Here, when an electric current is applied to the upper and lowerelectrodes 68, 60, the piezoelectric plate 62 is contracted. At thistime, the resilient plate 70 attached to the piezoelectric plate 62 isdeformed in a downwardly convex shape and thus exerts a pressure to thechamber.

Due to the pressure exerted to the chamber 78, the ink contained thereincan be discharged and sprayed through the nozzle 52 a, thereby carryingout a printing.

INDUSTRIAL APPLICABILITY

As described above, according to the piezoelectric ink jet printer headand its manufacturing process according to the invention, a chamber andink storage are integrally formed inside the ink jet printer head,thereby enabling a simple structure of the ink jet printer head.

In addition, the nozzle is formed of a single plate so that themanufacturing process can be simplified, thereby reducing themanufacturing cost and also improving the space efficiency.

Furthermore, the cross section leading to the nozzle from the chambervaries such that the amount of ink to be sprayed can be readilycontrolled, thereby allowing for the spraying of finer ink drops.

Also, the ink is supplied directly to each individual chamber via eachthrough-hole and ink passage provided in the side of the chamber,without necessity of a separate ink storage. Therefore, the space andarea, which otherwise would be occupied by a conventional ink storage,can be insignificantly saved, and the actuator and nozzle portion arearrayed in a two-dimensional pattern, thereby increasing the number ofnozzles, i.e., the nozzle density.

In addition, the ink is supplied directly to each individual chamber viaeach through-hole and ink passage provided in the side of the chamber.Therefore, the size of the chamber can be reduced and the ink passagewaycan be simplified, thereby significantly reducing the possibility ofentrapping ink bubbles therein.

While the present invention has been described with reference to theparticular illustrative embodiments, it is not to be restricted by theembodiments but only by the appended claims. It is to be appreciatedthat those skilled in the art can change or modify the embodimentswithout departing from the scope and spirit of the present invention.

1. A piezoelectric ink jet printer head comprising: an actuator comprising an upper upper electrode, a lower electrodes, a piezoelectric plate between the upper electrode and the lower electrodes, a protection layer over the upper electrode, and a resilient plate below the lower electrode; a spacer below the resilient plate, wherein a first portion of the spacer forms sidewalls of a chamber and a second portion of the spacer an upper surface of an ink passage; a channel plate below the spacer, wherein a first portion of the channel plate forms a sidewall of the ink passage under the second portion of the spacer and a second portion of the channel plate forms a sidewall of the chamber; a nozzle plate below the channel plate, wherein a first portion of the nozzle plate forms a bottom surface of the chamber and a second portion of the nozzle plate forms a bottom surface of the ink passage; a nozzle at a bottom portion of the chamber; and a through-hole formed through the actuator and the spacer reaching the ink passage, wherein the through-hole is configured to supply ink to the chamber via the ink passage.
 2. The piezoelectric ink jet printer head according to claim 1, wherein the bottom portion of the chamber is tapered around the nozzle.
 3. The piezoelectric ink jet printer head according to claim 1, comprising an ink container above the actuator, wherein the ink container is configured to supply ink to the chamber through the through-hole and the ink passage.
 4. The piezoelectric ink jet printer head according to claim 1, wherein the resilient plate comprises ZrO₂.
 5. The piezoelectric ink jet printer head according to claim 1, wherein the resilient plate comprises BaTiO₃.
 6. The piezoelectric ink jet printer head according to claim 1, wherein the resilient plate comprises Al₂O₃.
 7. The piezoelectric ink jet printer head according to claim 2, wherein the bottom portion of the chamber tapered around the nozzle to allow ink to flow down to the nozzle.
 8. The piezoelectric ink jet printer head according to claim 3, wherein: the piezoelectric printer head is comprised in a plurality of ink jet heads; and said plurality of ink jet heads are arranged in a matrix array in substantially the same plane; and each of said plurality of ink jet heads is configured to receive ink from the ink container.
 9. The piezoelectric ink jet printer head according to claim 1, wherein an upper portion of the through-hole is tapered in the actuator.
 10. The piezoelectric ink jet printer head accordingly to claim 1, wherein: width of the upper electrode is less than width of the lower electrode; and the through-hole intersects the lower electrode; and the through hole does not intersect the upper electrode. 